Environment files (.env) in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to load environment variables from a file named .env in Docker Compose.

Docker

services:
  app:
    env_file: [1]

Drag options to blanks, or click blank then click option'

Avariables.env

Bconfig.env

C.env

Denv.list

Attempts:

3 left

💡 Hint

Common Mistakes

Using a filename without the leading dot.

Confusing env_file with environment variables set directly.

The env_file option in Docker Compose specifies the file to load environment variables from. The default and common filename is .env.

2fill in blank

medium

Complete the .env file line to set the variable PORT to 8080.

Docker

PORT=[1]

Drag options to blanks, or click blank then click option'

A80

B8080

C8000

D443

Attempts:

3 left

💡 Hint

Common Mistakes

Adding quotes around the number.

Using a different port number.

In a .env file, variables are set as KEY=VALUE. To set PORT to 8080, write PORT=8080.

3fill in blank

hard

Fix the error in this .env line to correctly set the variable DEBUG to true.

Docker

DEBUG=[1]

Drag options to blanks, or click blank then click option'

Atrue

B"true"

CTRUE

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using capitalized or quoted boolean values.

Leaving spaces around the equals sign.

In .env files, boolean values are usually lowercase without quotes. So DEBUG=true is correct.

4fill in blank

hard

Fill both blanks to create a .env line that sets the variable API_KEY to a secret value.

Docker

API_KEY=[1][2]

Drag options to blanks, or click blank then click option'

A12345

Babcdef

C"

D'

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes for string values.

Using single quotes which may cause issues.

To set a string with letters in .env, wrap the value in double quotes: API_KEY="abcdef".

5fill in blank

hard

Fill all three blanks to write a Docker Compose environment section that uses the .env file and overrides PORT to 5000.

Docker

services:
  web:
    env_file: [1]
    environment:
      - PORT=[2]
      - DEBUG=[3]

Drag options to blanks, or click blank then click option'

A.env

B5000

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong filenames for env_file.

Setting PORT or DEBUG with wrong values or formats.

This Docker Compose snippet loads variables from .env and overrides PORT to 5000 and DEBUG to true in the environment section.

Practice

1. What is the main purpose of a .env file in Docker?

easy

A. To list all running Docker containers

B. To write Docker commands for building images

C. To store environment variables outside the Dockerfile for easy configuration

D. To define network settings for Docker

Solution

1. Step 1: Understand the role of .env files

   .env files hold environment variables separately from code or Dockerfiles, making it easy to change settings without editing code.

2. Step 2: Identify the correct purpose in Docker context

   Docker uses .env files to load environment variables into containers, not for commands, container lists, or network settings.

3. Final Answer:

   To store environment variables outside the Dockerfile for easy configuration -> Option C

4. Quick Check:

   .env files = environment variables storage [OK]

Hint: Think: .env means environment variables outside code [OK]

Common Mistakes:

• Confusing .env with Dockerfile commands
• Thinking .env lists containers or networks
• Assuming .env files run commands

2. Which of the following is the correct syntax for a line in a .env file?

easy

A. MY_VAR = value

B. MY_VAR: value

C. MY_VAR=>value

D. MY_VAR=value

Solution

1. Step 1: Recall .env file syntax rules

   Each line must be a key-value pair with no spaces around the equal sign, like KEY=value.

2. Step 2: Check each option

   MY_VAR=value uses no spaces and an equal sign, which is correct. The other options use spaces, colon, or arrow separators, which are incorrect.

3. Final Answer:

   MY_VAR=value -> Option D

4. Quick Check:

   KEY=value with no spaces [OK]

Hint: No spaces around = in .env lines [OK]

Common Mistakes:

• Adding spaces around equal sign
• Using colon or arrow instead of equal sign
• Using quotes unnecessarily

3. Given a .env file with content:

APP_NAME=MyApp
APP_PORT=8080

and a Docker Compose service using env_file: .env, what will be the value of APP_PORT inside the container?

medium

A. 8080

B. Not set

C. APP_PORT

D. MyApp

Solution

1. Step 1: Understand env_file usage in Docker Compose

   Docker Compose loads variables from the .env file and sets them as environment variables inside the container.

2. Step 2: Identify the value of APP_PORT

   The .env file sets APP_PORT=8080, so inside the container, APP_PORT will be "8080" as a string.

3. Final Answer:

   8080 -> Option A

4. Quick Check:

   APP_PORT = 8080 from .env [OK]

Hint: env_file loads variables exactly as key=value [OK]

Common Mistakes:

• Confusing variable names with values
• Assuming variables are not set inside container
• Mixing up APP_NAME and APP_PORT values

4. You have a .env file with the line DB_PASS=secret pass. When you run your Docker container, the environment variable DB_PASS is not set correctly. What is the likely problem?

medium

A. The space in the value causes parsing issues; values should not contain spaces without quotes

B. The key DB_PASS is invalid because it contains uppercase letters

C. The .env file must be named env.txt to work

D. Docker does not support environment variables from .env files

Solution

1. Step 1: Check .env file value format rules

   Values with spaces must be quoted or use no spaces; otherwise, parsing breaks.

2. Step 2: Identify the issue with the given line

   "secret pass" has a space but no quotes, so Docker reads only "secret" or fails to parse correctly.

3. Final Answer:

   The space in the value causes parsing issues; values should not contain spaces without quotes -> Option A

4. Quick Check:

   Spaces in values need quotes or no spaces [OK]

Hint: No spaces in values unless quoted in .env [OK]

Common Mistakes:

• Ignoring spaces in values
• Thinking uppercase keys are invalid
• Renaming .env file incorrectly

5. You want to use a .env file to set environment variables for multiple Docker Compose services, but one service needs a different value for API_URL. How can you handle this situation?

hard

A. Put all variables in one .env file and override the variable in the Dockerfile

B. Use multiple .env files and specify the correct one per service with env_file in each service definition

C. Use only one .env file and change the variable manually before running Docker Compose

D. Docker Compose does not support different env files per service

Solution

1. Step 1: Understand env_file usage per service

   Docker Compose allows specifying env_file separately for each service to load different environment variables.

2. Step 2: Apply multiple .env files for different services

   Create separate .env files with different API_URL values and assign them to each service using env_file.

3. Final Answer:

   Use multiple .env files and specify the correct one per service with env_file in each service definition -> Option B

4. Quick Check:

   Multiple env_files per service = different variables [OK]

Hint: Use separate env_file per service for different variables [OK]

Common Mistakes:

• Trying to override variables only in Dockerfile
• Editing one .env file manually each time
• Believing Docker Compose can't use multiple env files